1. Field of the Invention
The present invention relates to a propeller shaft for a vehicle, more particularly, to a vehicular propeller shaft capable of absorbing an impact by being deformed axially when an impact load is applied in the longitudinal direction of the vehicle.
2. Prior Art
Generally, a vehicle is constituted so as to transmit engine power from a transmission to a differential through a propeller shaft and from the differential to wheels.
However, the propeller shaft is disposed in the transversal center of the vehicle in the longitudinal direction thereof and therefore, for example, in an event of collision, when a large impact is exerted in the lengthwise direction of the vehicle, the deformation of the vehicle body is blocked by a "lengthwise resistance" of the propeller shaft and as a result a still larger impact is caused in the vehicle.
In order to solve this problem, Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-178105 discloses a technique in which a propeller shaft is shaped into a hollow pipe to raise a torsional rigidity per weight. Also, the propeller shaft has a swelling portion annually formed in the radial direction thereof. When an excessively large impact load is applied to the vehicle, the swelling portion is deformed so that the propeller shaft is released from a state of lengthwise resistance.
As shown in FIG. 8, List of Unpatentable Examples of Automobile Technologies No. 95202 published by the Committee of Intellectual Properties of Japan Automobile Manufactures Association, discloses a propeller shaft 100 comprising a hollow propeller shaft 101, a center support bearing 102 provided at the rear end of the propeller shaft 100 and a bellows pipe 103 connected in the front thereof with the hollow propeller shaft 101 and connected in the rear thereof with the center support bearing 102. When an axial load is applied to the propeller shaft 100, the bellows pipe 103 is deformed so that the propeller shaft 100 can be released from the state of lengthwise resistance.
Further, FIG. 9a shows a propeller shaft 111 disclosed by Japanese Patent Application Laid-open No. Toku-Kai-Hei 8-226454. The propeller shaft 111 comprises a female member 112 and a male member 113 spline-fitted to the female member 112. The female member 112 comprises a small diameter portion 112a and a large diameter portion 112b and the small diameter portion 112a is spline-fitted over the male member 113. Therefore, a step portion 112c is formed on the propeller shaft 111 between the small diameter portion 112a and the large diameter portion 112b.
When an impact load is applied to thus formed propeller shaft 111 in the longitudinal direction, as shown in FIG. 9b, the step portion 112c is deformed or broken in the axial direction so as to absorb the impact load.
According to the propeller shaft disclosed in the Patent Application No. Toku-Kai-Hei 5-178105, when a large impact load is applied in the longitudinal direction, first the swelling portion must be deformed in the axial direction. However, the deformation of the swelling portion needs a large initial load and therefore the impact can not be absorbed in a proper and effective way. Further, there occurs so called "collision phenomenon" in which both ends of the swelling portion abut against each other and as a result the propeller shaft can not have an adequate crash stroke. On the other hand, the formation of a plurality of swelling portions leads to a fear of reduced critical speed of the propeller shaft.
In case of the propeller shaft 100 disclosed in List of Unpatentable Examples of Automobile Technologies No. 95202, when an axial load is exerted on the hollow propeller shaft 101, the bellows pipe 103 is deformed to reduce the lengthwise resistance of the propeller shaft 100.
However, when the propeller shaft 100 is deformed and shortened, respective tops of the bellows pipe 103 abut against neighboring tops and respective valleys thereof abut against neighboring valleys, that is, "collision phenomenon" is generated. This prevents the propeller shaft 100 from having an adequate crash stroke. On the other hand, an increased number of tops and valleys of the bellow pipe 103 has an adverse effect on the critical speed of the propeller shaft 100.
According to the propeller shaft 111 disclosed in Toku-Kai-Hei 8-226454, the problem is that since the deformation or breakage in the axial direction requires a large impact load, especially, a large impact load at the initial stage, the propeller shaft 111 still has a difficulty in alleviating the impact effectively.